Cooling system



F. LAMBRECHT COOLING SYSTEM June 23, 1970 2 Sheets-Sheet 1 Filed April 25. 1968 MW L/W/WL'C'H T June 23, 1970 F. LAMBRECHT 3,516,390

COOLING SYSTEM Filed April 25, 1968 2 Sheets-Sheet 2 PM 2 A m/(H HT dim 1,

United States Patent U.S. Cl. 1227 12 Claims ABSTRACT OF THE DISCLOSURE A cooling system for a waste-heat boiler which is intermittently heated, such as, for example, for the waste-heat boiler of a converter where the boiler is exposed to intense heating during the blow periods, and to relatively low heat during the off-blow periods. The cooling system is composed of a plurality of units one of which is subjected to heat which is more intense than that to which the remainder of the system is exposed, this one unit, which would be the converter hood in the case of a converter installation, being cooled by a means which provides a forced through-flow of a cooling fluid during the perods of intense heat, such as the blow periods in the case of a converter, and which provides a forced circulation of the cooling fluid during the alternating periods of low heat, which would be the off-blow periodu in the case of a converter.

CROSS REFERENCE TO RELATED APPLICATION This .application is a continuation-in-part of copending application Ser. No. 701,968, filed Jan. 31, 1968, entitled Cooling System, now abandoned.

BACKGROUND OF THE INVENTION The invention relates to a cooling system for a Wasteheat boiler which is intermittently heated.

In particular, the invention relates to a cooling system which is adapted for use with the waste-heat boiler assembly of a converter installation. It is already known to cool waste-heat boilers with a system according to which the cooling fluid circulates naturally. However, the construction and shape of the waste-heat boiler creates in this case certain difficulties which in many cases make it impossible to provide a proper layout of the tubes without creating problems in connection with the natural Water circulation.

There are also known installations where a waste-heat boiler is cooled with a forced circulating system. However, in this case with increasing sizes of the boilers increasing amounts of cooling liquid must be circulated, so that large circulating pumps are required. In addition to the large first costs involved in purchasing and installing such pumps, there is also a large consumption of energy required for such pumps, so that the operating costs are undesirably high in such cases. In the case of 100 ton converter and waste-heat boiler installation, it is required to provide circulating pumps which must pump up to 1400 tons/hour of water (approximately 310,- 000 gallons/ hour), with a pressure increase of approximately 6 atmospheres.

It is also known to construct waste-heat boilers which are cooled according to a forced-through flow system. However, such a system cannot readily be used, without special measures, for a waste-heat boiler, particularly for the waste-heat boiler installation of a converter or lime kiln, because the generation of steam and supply of heat do not correspond to the feeding of the waste-heat boiler which is intermittently heated, so that if it should hap- 3,516,390 Patented June 23, 1970 pen that the amount of cooling fluid flowing through this system is too small there is the danger of localized excessive wall temperatures.

SUMMARY OF THE INVENTION It is, therefore, a primary object of the present invention to provide a cooling system which will avoid the the above drawbacks.

In particular, it is an object of the invention to provide a cooling system which can be used with waste-heat boilers which are subjected to periods of intense heat which alternate with periods of low heat, as is the case with waste-heat boilers of converters, for example.

Thus, it is an object of the invention to provide a cooling system which is simple and highly reliable in operation while at the same time avoiding any possibility of localized excessive heating.

Also, it is an object of the present invention to provide a cooling system which greatly reduces the amount of cooling fluid which must be circulated.

Also, an object of the present invention resides in providing suitable controls, which may be automatic, for the cooling system.

Thus, according to the invention the cooling system is composed of a plurality of units one of which is exposed to a heat which is more intense than the remainder of the system, and in the case of a converter installation it would be the converter hood which is exposed to the most intense heating. The waste-heat boiler is intermittently heated during periods of intense heat which alternate with period of low heat. In accordance with the invention that unit of the system which is exposed to the most intense heat is cooled during the periods of intense heat with a forced through'flow cooling system and during the alternating periods of relatively low heat with a forced circulating system. Thus, in the case of the waste-heat boiler of a converter, during the blow periods the hood is cooled with a forced-through flow of the cooling fluid while during the oifblow periods, the hood is cooled with forced circulation of the cooling fluid. That part of the system which is not exposed to the most intense heat is cooled, in accordance with a further feature of the invention, by a natural circulation system.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is illustrated by way of example in the accompanying drawings which form part of this application and in which:

FIG. 1 is a schematic illustration of the cooling system of a converter waste-heat boiler;

FIG. 2 is a schematic illustration of a modification of the system of FIG. 1; and

FIG. 3 is a schematic illustration of a converter wasteheat boiler installation for a pair of steel converters.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring now to FIG. 1, there is schematically illustrated therein the connections of the various components of a waste-heat boiler installation provided with a pair of flues. The waste-heat boiler installation includes the suction hood 1, the radiation flue 2, and the convection flue 3. The hot waste gases which flow upwardly out of the converter 12 are received in the suction hood 1 and are partially cooled at the cooling surfaces 6 formed by the tubes of the hood 1, these surfaces 6 forming radiation surfaces. The waste gases flow from the hood 1 through the radiation flue 2 into the convection flue 3 Where these gases are further cooled. The inlet end of the convection flue 3 communicates with the outlet end of the radiation flue 2. At its outlet end the convection flue 3 communicates with an unillustrated dust collector installation and a discharge stack through which the waste 3 gases can be discharged to the atmosphere. The radiation flue 2 and convection flue 3 are covered at their interiors with heating surfaces 4 and '5 formed by the exterior surfaces of tubes through which coolant in the form of a suitable cooling liquid flows according to a natural circulation means air system. The coolant which flows through the tubes which form the exterior heating surfaces 4 and 5 will in general be water or a water-steam mixture or water vapor. The cooling fluid provided in the boiler for cooling by natural circulation is derived from a boiler drum 14 which is connected in common to the units 2, 3 of the system which are subject to lesser heat than the unit 1 thereof, the natural circulation being provided by way of heat from the surfaces 6 of the unit 1 which are radiation surfaces as pointed out above.

Thus, these heating surfaces 6 formed by the tubes of the hood 1 are exposed to the most intense heat, the tubes which form the hood 1 being situated in side by side relation so that their inner exterior surfaces form the heating surfaces 6. During the blow periods of the converter 12, which are the intermittent periods of intense heat, there is a forced through-flow cooling of the unit 1 by flow of coolant in the tubes thereof which form the surfaces 6, while during the alternating periods of relatively low heat, which are the off-blow periods, when only a relatively small amount of heat must be carried away, as when, for example, at the end of a blow period there are still a few minutes during which glowing particles of slag cling to the tubes, the cooling takes place by way of a forced circulation of the cooling fluid. During the heating of the hood 1 the boiler is fed from a feedwater container 7 through a feedwater pump 8. The feedwater container is supplied with fresh water from an unillustrated feedwater preparing installation or from a feedwater pre-heating installation.

As is apparent from FIG. 1, the cooling fluid flows from the pump 8 through the last set of tubes 13 of the convection flue 3 at the region where the gas is discharged from the convection flue 3 and where the cooling at this outer region of the flue 3 takes place, so that in this way the cooling liquid which is fed to the hood 1 is pre-heated to be supplied in this condition into the interior of the tubes which provide the hood 1 with its inner heating surfaces 6. The connection between the hood 1 and the tubes 13 can be reversed, however, so that the cooling liquid supplied from the pump 8 will initially flow through the tubes of the hood 1 and then through the set of tubes 13 at the outlet region of the convection flue 3.

The cooling liquid or steam-water mixture, after flowing through the tubes 13 and the tubes of the hood 1, flow in partly vaporized condition into the boiler drum During the off-blow periods of relatively low heat, the feed pump 8 does not operate. The stopping of the operation of the feed pump 8 during the periods of low heat takes place automatically as soon as the bath of steel in the converter has the desired composition, this termination of the operation of the pump 8 taking place in parallel and simultaneously with the termination of the blast of oxygen through the lance into the steel bath, so that the pump 8 is controlled simultaneously with the control of the oxygen blast. However, these controls can also be brought about manually, simultaneously with control of the supply of oxygen through the lance, from the panel at the pulpit of the converter installation by way of an electrical conductor 30 schematically shown in FIG. 1 connected to the pump 8 so as to control the latter. This latter control may be used in addition to or replaced by a control through a conductor 31 depending upon the elevation of the liquid level 32 in the boiler drum 14 in such a way that when the liquid in the drum 14 reaches its highest elevation the circuit of the pump 8 is automatically opened so as to stop the operation of the pump, while when the lever of the liquid in the boiler drum 14 reaches its lowest elevation the pump 8 again has its control circuit closed so that it is automatically set into operation. Thus, it is through the pump 8 that a forced through-flow type of cooling for the unit 1 is achieved during the blow periods of intense heat.

During the off-blow periods of relatively low heat there is a momentary stagnation of the cooling liquid in the tubes 13, and a circulating pump 9, which is constantly in operation, takes over the cooling of the hood 1, upon termination of the forced through-flow from the pump 8, this cooling derived from the circulating pump 9 being a forced circulation of coolant by maintenance through the circulating pump 9 of a minimal amount of coolant circulating through the unit 1. During the periods when the feed pump 8 operates, the pressure of the liquid resulting from the action of the pump 8 is greater than the pressure provided by way of the circulating pump 9, so that the greater pressure of the forced through-flow circulation from the pump 8 renders the forced circulation derived from the pump 9 ineffective during the periods of intense heat.

It is also possible to provide an arrangement where the circulating pump 9 operates alternately with the feed pump 8, the connections to these pumps being such that one of these pumps is always in operation so that whenever the pump 8 is not operating the pump 9 is automatically set into operation to continue the cooling by way of forced circulation, whereas when the pump 9 stops operating the pump 8 is automatically set into operation to provide the forced through-flow type of cooling.

The circulating pump 9 sucks water from the boiler drum 14 through hte conduit 19, and this cooling liquid is delivered under pressure from the pump 9 to the tubes of the unit 1, the circulating pump 9 also serving to pump the cooling fluid from the unit 1 through the conduit 20 back into the drum 14. The pressure outlet of the circulating pump 9 communicates with the inlet ends of the tubes of the unit 1 through a header 21, while the outlet ends of the tubes of the unit 1 communicate through a header 22 with the return conduit 20. These headers 21 and 22 are in the form of circular rings communicating with the several tubes which form the surfaces 6 of the unit 11. In order to prevent a return flow of the cooling liquid during operation of the feed pump 8, a non-return valve 11 is situated in the pressure outlet conduit 10 of the circulation pump 9. With the structure of the invention it is possible to reduce the circulation output with a waste-heat boiler of the same size to about 50 tons/hour (approximately 11,000 gallons/hour), as compared to the above-mentioned circulation of 1400 tons/hour (approximately 310,000 gallons/hour). There is also a significantly smaller pressure loss of approximately one half atmosphere.

FIG. 2 illustrates an embodiment of a waste-heat boiler having a suction hood 1 whose cooling surfaces 6 are cooled according to a system which differs from that of FIG. 1. From the feedwater container 7 there is a conduit leading to the feed pump 8 which can be regulated. The regulation of the feed pump 8 takes place according to the metallurgical conditions in the converter 12, particularly in accordance with the raw iron composition and the amount thereof when the oxygen blast begins, or from the anticipated manner in which the process will progress by way of a control conductor 30. The fine regulation of the feed pump 8 takes place depending upon the temperature or moisture content of the cooling liquid or steam-water mixture which discharges from the header 22, this control for the pump 8 being provided by way of the electrical conductor 33. The feed pump 8 feeds the water under pressure, to provide forced through-flow during the blow periods, through the conduit 23 into the header 21 through which the cooling liquids enters the hood 1. From the header 21 the cooling liquid flows through the cooling tubes of the hood 1 into the discharge header 22. The heating surfaces 6 formed by the tubes of the hood 1 can be connected to further heating surfaces of further tubes until vaporization takes place.

In the conduit 24, which connects the header 22 with the boiler drum 14 and in some cases with further heating surfaces, there is a valve means 26 which maintains a minimum amount of cooling fluid in the circuit. This Valve 26 is controlled by a control unit 25 in such a way that when the generation of steam drops a return flow of excess feedwater back to the feedwater container through a reducing unit is made possible. This control 25 consists essentially of a temperature measuring device and/ or a moisture content measuring device for the medium which leaves the unit 1 or the header 22. This control structure influences the feed pump 8 during the blow period so as to regulate the feed pump 8, and it influences during the off-blow periods the valve 26 which maintains a minimum amount of liquid in circulation, so that the cooling liquid which during the off-blow periods can no longer be vaporized, returns to the feedwater container. Thus, with this construction a minimum amount of cooling liquid circulating through the tubes of the unit 1 is always assured independently of the particular generation of steam at any given moment. The heat content of the returned feedwater can advantageously be used for degassing the feedwater or may be used to compensate for the radiation losses of the feedwater container 7. In this way also a precooling of the feedwater before it reaches the suction inlet of the pump 8 is achieved. The return flow of the cooling liquid takes place through a conduit 27, so that an additional supply of feedwater is delivered to the container 7 during the off-blow periods, this latter supply being in addition to that which is provided in the normal way from the usual feedwater preparing or feedwater preheating installation.

At the region of the entrance of the waste gases into the radiation flue 2, of the boiler installation, there is a coarse slag catcher unit 28 for relatively large slag particles, this slag catcher 28 taking the form, in particular, of a tubular field grid through which the cooling medium flows in a manner similar to the flow of the cooling medium through the tubes of the unit 1. The feed pump 8 is controlled, either by way of the control device 25 or from the metallurgical conditions in the converter, in such a way that during the peak" blow periods a maximum amount of cooling liquid flows by forced throughflow through the tubes of the unit 1 which form the inner heating surfaces 6 thereof, while during the off-blow periods only a relatively small amount of feedwater is delivered'to the boiler unit 1 with forced circulation taking place at this time by way of the return conduit 27 in the manner described above. Thus, in this case also the feeding of the waste-heat boiler takes place in an irregular manner from the converter hood 1.

The waste-heat boiler installation which is illustrated in FIG. 3 is designed for a plurality of fixed or movable converters, a pair of these converters being shown in the illustrated example. In the illustrated waste-heat boiler there are a pair of hoods 1 through which the hot waste gases from the converters 12 flow alternately and never simultaneously. The hoods 1 communicate with the flue Z to deliver the flue gases thereto, and it is in the flue 2 that the heating surfaces 4 and 5 of the natural circulation cooling system are situated. The particular hood 1 which at any given moment is not heated is cut off from communication with the vertical boiler flue 2 at the inlet end of the latter by way of a closure means 29 which can take the form of a suitable valve or, as shown in the drawing, of a tiltable damper or plate. This closure means 29 can advantageously be cooled and for this purpose valves 34 which control the flow of cooling liquid from the heat pump 8 t0 the pair of hoods 1, respectively, and these valves are combined with non-return valves and are controlled from the pulpit either manually or automatically according to whichever converter is in operation. It is possible, however, to also provide automatic controls for the valves 34 in accordance with the temperature of the fluid which discharges from the headers 22. Thus, when the temperature of the cooling medium in a discharge header 22 rises, and such a rise in temperature takes place as soon as a converter has been placed in its upright position with a new charge of iron and before the beginning of the oxygen blast, the valve 34 connected to the hood which communicates with the particular outlet header 22 is automatically opened.

The control for the feed pump 8 then takes place in a manner similar to that described above in connection with FIG. 1, depending, for example, upon the height of the liquid in the boiler drum 14.

The cooling liquid flows through the conduit 16 into the supply header 17 of one or the other of the hoods 1, and from the supply header the cooling liquid flows into the tubes of the particular hood to have heat trans ferred through the heating surfaces 6. The discharging hot water or steam-water mixture flows through the conduit 18 into the boiler drum 14 where the boiler unit 2, 3 is connected to be provided with the cooling by natural circulation, as pointed out above. The particular interconnection of the boiler components 2 and 3 is not illustrated. During the off-blow periods, the hood 1 of the converter which is not in operation has its connection with the feed pump cut oif and now the continuously operating circulating pump 9 takes over the cooling of this latter hood 1. At the instant when the relatively high pressure of the feedwater pump 8 no longer acts upon the non-return valve 35 in the outlet pressure conduit of the circulating pump 9, this latter valve opens automatically without any exterior actuation. The continuously operating circulating pump 9 now takes over the cooling function formerly provided by Way of the feed pump 8. Theoretically there is also the possibility of opening a valve 35 when its corresponding valve 34 closes, so that there is no interruption in the flow of cooling medium.

The circulating pump 9 sucks water through the conduit 15 from the boiler drum 14 and this water is delivered under pressure through the conduit 16 to the tubes of the hood 1 which at this instant communicates with a non-operating converter, the steam-water mixture then returning from the latter hood 1 to the boiler drum 14.

It is to be noted that with this construction the changeover from forced through-flow to forced circulation takes place independently in the pair of hoods 1. Thus, this changeover takes place depending upon the heating intensity. Thus, with this construction the converters operate fully independently of each other, but their blow periods do not overlap to any appreciable extent, so that the control can take place in a simple manner in accordance with which of the hoods 1 is about to be subjected to a period of intense heating. The primary impulse which controls the feed pump 8 thus is derived, as mentioned above, from the control of the supply of the oxygen blast or from the level of the liquid in the boiler drum. During the alternate operation of the pair of converters there is also a cyclical alternating of the types of cooling systems used with the particular hoods 1. In the event that there is an additional firing installation 36, particu larly an additional oil firing installation, it is of advantage to provide for cooling only of the hoods and the closure means 29 according to the alternating systems of forced circulation and forced through-flow.

The invention is not to be considered as limited in its utility to converters. The periods of high heat intensity are not to be understood as being only the blow periods of converter installations. The intermittent heating can also include periods of intense heating which need not necessarily be determined by the blow periods. The invention can advantageously also be used with wasteheat boilers of lime kilns. A further possibility of use of the invention is in connection with a waste-heat boiler for firing of blast furnace gas in steel mills.

What is claimed is:

1. In a system for cooling a waste-heat boiler which is intermittently heated so as to have periods of intense heat which alternate with periods of low heat, such as a converter waste-heat boiler, a plurality of units coacting together to form the cooling system and including one unit which is heated more intensely than the remainder of the cooling system, a feedwater container and means coacting with said one unit for providing a forced-through flow of cooling fluid only from said feedwater container through said one unit during the periods of intense heat and for providing a forced circulation of fluid therethrough during the periods of low heat, whereby in the case where said one unit is a converter hood, forced-through flow of coolant takes place in the hood during blow periods and forced circulation takes place during off-blow periods.

2. In a system for cooling a waste-heat boiler which is intermittently heated so as to have periods of intense heat which alternate with periods of low heat, such as a converter waste-heat boiler, a plurality of units coacting together to form the cooling system and including one unit which is heated more intensely than the remainder of the cooling system, and means coacting with said one unit for providing a forced-through flow of cooling fluid therethrough during the periods of intense heat and for providing a forced circulation of fluid therethrough during the periods of low heat, whereby in the case where said one unit is a converter hood, forcedthrough flow of coolant takes place in the hood during blow periods and forced circulation takes place during off-blow periods, and a natural circulation means coacting with said remainder of said system which is not exposed to the most intense heat to be cooled with natural circulation of coolant through said remainder of said system.

3. The combination of claim 1 and wherein a boiler drum is common to and operatively connected with said units of said system, said boiler drum forming a part of said means which provides forced circulation of fluid during the periods of low heat, and the latter part of said means also including a circulating pump communicating with said boiler drum.

4. The combination of claim 1 and wherein said means provides during said periods of low heat a lesser amount of cooling fluid than during the periods of intense heat.

5. The combination of claim 4 and wherein said one unit has heating surfaces through which heat is transferred for purposes such as preheating or steam generation.

6. The combination of claim 2 and wherein during the periods of intense heat the remainder of said system which is cooled by natural circulation communicates with said one unit to be supplied with coolant from said one unit.

7. The combination of claim 1 and wherein said means includes a circulating pump which operates constantly during said periods of intense heat and said periods of low heat.

8. In a system for cooling a waste-heat boiler which is intermitttntly heated so as to have periods of intense heat which alternate with periods of low heat, such as a converter waste-heat boiler, a plurality of units coacting together to form the cooling system and including one unit which is heated more intensely than the remainder of the cooling system, and means coacting with said one unit for providing a forced-through flow of cooling fluid therethrough during the periods of intense heat and for providing a forced circulation of fluid therethrough during the periods of low heat, whereby in the case where said one unit is a converter hood, forced-through flow of coolant takes place in the hood during blow periods and forced circulation takes place during oil-blow periods, said means including a circulating pump and a means for automatically setting said latter pump into operation at the end of each period of intense heat and for automatically stopping said circulating pump at the end of each period of low heat.

9. In a system for cooling a waste-heat boiler which is intermittently heated so as to have periods of intense heat which alternate with periods of low heat, such as a converter waste-heat boiler, a plurality of units coacting together to form the cooling system and including one unit which is heated more intensely than the remainder of the cooling system, and means coacting with said one unit for providing a forced-through flow of cooling fluid therethrough during the periods of intense heat and for providing a forced circulation of fluid therethrough during the periods of low heat, whereby in the case where said one unit is a converter hood, forced-through flow of coolant takes place in the hood during blow periods and forced circulation takes place during oif blow periods, the waste-heat boiler including a plurality of hoods and converters with which said hoods respectively communicate, and said means coacting with said hoods for providing at each hood a changeover from forced-through flow to forced circulation independently of the operations at any other hood and depending only upon the operating conditions of the converter of each hood.

10. The combination of claim 9 and wherein an adjustable closure means coacts with said hoods at the lo cation of the communication thereof with the remainder of said system for selectively closing and opening the communication between the hoods and the remainder of said system.

11.In a system for cooling a waste-heat boiler which is intermittently heated so as to have periods of intense heat which alternate with periods of low heat, such as a converter wasteheat boiler, a plurality of units coacting together to form the cooling system and including one unit which is heated more intensely than the remainder of the cooling system, and means coacting with said one unit for providing a forced-through flow of cooling fluid therethrough during the periods of intense heat and for providing a forced circulation of fluid therethrough during the periods of low heat, whereby in the case where said one unit is a converter hood, forced-through flow of coolant takes place in the hood during blow periods and forced circulation takes place during off-blow periods, a feedwater container and feedwater pump forming part of said means, said means including a throttling means for throttling said feedwater pump during said period of low heat, and said means further including a valve means for returning excess feedwater to said feedwater container when the amount of feedwater corresponding to a given steam output falls below a minimum amount required for cooling.

12. In a system for cooling a waste-heat boiler which is intermittently heated so as to have periods of intense heat which alternate with periods of low heat, such as a converter waste-heat boiler, a plurality of units coacting together to form the cooling system and including one unit which is heated more intensely than the remainder of the cooling system, and means coacting with said one unit for providing a forced-through flow of cooling fluid therethrough during the periods of intense heat and for providing a forced circulation of fluid therethrough during the periods of low heat, whereby in the case Where said one unit is a converter hood, forced-through flow of coolant takes place in the hood during blow periods and forced circulation takes place during off-blow periods, said means including a feedwater pump, means for throttling the latter during said periods of low heat, valve means for returning to a suction inlet 'of said feed I pump excess feedwater when the amount of feedwater cor- FOREIGN PATENTS responding to a given steam output falls below a predetermined minimum amount required for cooling, and means for precooling the excess feedwater before return 897,724 5/ 1962 Great Britain.

thcfeof to id f d t Pump KENNETH W. SPRAGUE, Primary Examiner 5 References Cited s CL UNITED STATES PATENTS 122. 40

3,234,920 2/1966 Kemmetmuller et a1. 122-7 

